Determination of Respiratory LD 30 from Number of Primary Lesions as Illustrated by Melioidosis. ∗

Summary

1. A method is described whereby the respiratory LD₅₀ can be obtained from the dose of organisms inhaled and from counts of primary pulmonary lesions, provided a single pulmonary lesion is fatal and progressing primary lesions do not occur elsewhere. This method was tested and confirmed in experimental melioidosis in mice and hamsters, and its advantages over the usual titration method were discussed. 2. The number of M. pseu-domallei necessary to generate one lesion, called the “ratio,” is obtained by dividing the inhaled dose by the total number of primary pulmonary foci. This “ratio” multiplied by 0.7 equals the respiratory LD₅₀. Data and graphs are presented to estimate the total number of primary pulmonary lesions when they are so numerous that only the lesions on the surface of the lung can be counted. Estimates of the 95% confidence interval of the respiratory LD₅₀ obtained by this lesion-count method overlapped those obtained by the titration method.

We wish to acknowledge the statistical advice of Mr. Leonard Goldberg, the technical assistance of Roy Forcier, HMC., and William Eisenman, HM3, as well as the aid of Dr. Clara Nigg in the preparation of the manuscript.